Quick Guide to Precision Measuring Instruments
PG71Quick Guide to Measurement• CeramicThis material is mainly used for styli because of its high stiffness to mass ratio. It has excellent thermal stability and is not affected by the temperature environment, thereby allowing higher accuracy measurement.• Carbon fiberCarbon fiber is a material appropriate for long styli since the mass of a carbon fiber stylus is approximately 20% of that of a carbide stylus. Thanks to excellent thermal stability, a carbon fiber stylus is little affected by the operating environment. • CalibrationEven if a stylus appropriate for a workpiece is selected, an accurate measurement result will not be obtained unless the probe to be used is calibrated prior to measurement, which involves probing a master reference sphere in a defined sequence so that the CMM software can establish the ball tip and probe/stylus characteristics.• Calibration mechanismThe CMM calculates the center position and diameter of each stylus ball using the specific probe calibration program.This program uses CMM measurements made of the reference sphere with each configured stylus ball to determine the true diameters of the balls and stores the measured data in the software. The precise diameter of the reference sphere is known from a previous calibration measurement and is also stored for use in the calculations. As a workpiece may be measured from every direction, a stylus is calibrated with measurements at multiple points on the reference sphere. A scanning system needs to obtain a large number of points for calibration. With these procedures observed, the effective dia-meter for each stylus ball and the center positions of the stylus balls in the machine coordinate system are set to enable accurate measurement.2. Ball TipSelection of the most suitable ball tip material involves taking the measuring procedure and workpiece material into account.• RubyA ruby ball provides a particularly hard, smooth surface, featuring high compressive strength and excellent mechanical wiping.A ruby is appropriate as a ball material for scanning diverse workpieces, but may cause abrasion during the scanning measurement of alumi-num and cast iron. In this case, it is advisable to use other materials as listed below. • Silicone nitrideSilicon nitride, which is similar to ruby, is a ceramic material that provides high hardness and strong resistance to abrasion. Since silicon nitride will not fuse with aluminum, so will not cause adhesive wear like ruby. However, it is recommended that a silicon nitride ball be used only for aluminum workpieces due to a marked susceptibility to abrasion on steel surfaces. Note: This material is available by custom order.• ZirconiaZirconia is a ceramic material that demonstrates a particularly outstanding hardness and has hardness and abrasion characteristics equivalent to a ruby. A zirconia ball is optimal for scanning cast iron workpieces because of its non-abrasive characteristics with this material. Note: This material is available by custom order.